Project Summary/Abstract Synaptic plasticity is thought to be a basis of learning and memory of the brain. Signaling mechanisms underlying synaptic and behavioral plasticity have been extensively studied with the aid of pharmacological and genetic manipulation of signaling. However, it has been difficult to assess the spatiotemporal aspects of signaling activity particularly. The goal of this proposal is to develop a new technique based on genetically encoded light- inducible kinase inhibitors to resolve the spatiotemporal dynamics of signaling required for synaptic and behavioral plasticity in vivo. Our preliminary data using a newly- developed photo-inducible CaMKII inhibitor demonstrates that ~60 s of CaMKII activity is sufficient to induce structural plasticity of dendritic spines. We aim to 1) develop photo- inducible inhibitors for kinases including CaMKII, PKC and PKA, 2) determine the timing of kinase activity required for synaptic plasticity in slices, and 3) identify the spatiotemporal window of kinase activity required for learning-related dendritic spine turnover in vivo and animal?s performance improvement after learning. The new tool will provide new insights into the action of kinases in vivo during synaptic and behavioral plasticity.